Coaxial magnetron

ABSTRACT

A coaxial magnetron having a cylindrical cavity operating in a circular mode is tuned by means circumferentially disposed in the region of maximum electric field intensity. In one embodiment a ring tuner is retained within an annular groove at the midpoint of the outer cavity wall and adapted to be reciprocated in introduce a dissymmetry in the cavity geometry along a path transverse to its axis. The paths of the electric field currents are altered by each excursion of the tuner. Dither tuning of the disclosed structure provides a frequency agility in transmission systems over a portion of the frequency band. Another embodiment provides for the combination with a large plate-type tuner to add a fine tuning capability over a portion of a broad frequency band. Temperature compensation is also attainable by means of the ring tuner arrangement.

W333 @Wte Foreman [54] COAXHAL MAGNETRON [56] References Cited UNITEDSTATES PATENTS 3,333,148 7/1967 Buck "315/3977 X 2,466,060 4/1949Spencer.... ..3l5/39.77 X 12/1968 Powell ..315/39.77 X

[ 51 May 1, N73

Primary Examiner-Rudolph V. Rollinec Assistant Examiner-*SaxfieldChatmon, Jr. Attorney-Harold A. Murphy et al.

[57] ABSTRACT A coaxial magnetron having a cylindrical cavity operatingin a circular mode is tuned by means circumferentially disposed in theregion of maximum electric field intensity. in one embodiment a ringtuner is retained within an annular groove at the midpoint of the outercavity wall and adapted to be reciprocated in introduce a dissymmetry inthe cavity geometry along a path transverse to its axis. The paths ofthe electric field currents are altered by each excursion of the tuner.Dither tuning of the disclosed structure provides a frequency agility intransmission systems over a portion of the frequency band. Anotherembodiment provides for the combination with a large plate-type tuner toadd a fine tuning capability over a portion of a broad frequency band.Temperature compensation is also attainable by means of the ring tunerarrangement.

12 Claims, 11 Drawing Figures PATENTEDHAY' 1 ma SHEET 1 OF PATENTEDNAY-H 7 3,731,137

SHEET 2 BF 6 MAGNET MAGNET RING DISPLACEMENT (Ml L5) 0 2O 4O 6O 8OFREQUENCY DEVIATION MHZ PATENTEDHAY 1 ms SHEET 6 BF 6 H1, am .1. an. M

COAXIAL MAGNETRON BACKGROUND OF THE INVENTION The invention relates tocrossed field electron discharge devices of the coaxial magnetron typeand, in particular, to a tuning structure for such devices.

US. Pat. No. 2,854,603 issued Sept. 30, 1958, to RJ. Collier and J.Feinstein discloses a coaxial magnetron device having an inner and anouter resonant system. The inner system comprises a plurality ofradially extending vane members extending from an anode wall definingtherebetween resonant cavities circumferentially disposed around acentral cathode. An outer system is defined by an annular wall memberand the cylindrical anode wall to provide an outer circular coaxialcavity resonator. Coaxial magnetrons generally provide for the outercavity resonator to operate in the TE circular electric and magneticmode. Electromagnetic energy is coupled from alternate inner cavityresonators by slots extending within the common anode boundary wall. Theinner system generally operates in the pi-mode and the coupling slotstogether with slot mode absorbing structures are dimensioned to providefor efficient coupling of the respective modes.

In the prior art, such devices have been tuned by an annular platemember which is axially movable within the external cavity resonator.The tuning member effectively forms a movable end wall of the cavityresonator. As it is actuated in a direction towards the opposing endwall member the volume of the cavity is altered. An example of a priorart plate-type tuning struc- I reed elements of the type disclosed inU.'S. Pat. No.

3,087,124, issued Apr. 23, 1963, to- Willard M. McLeod, Jr. Spinningtype'structures have also been disclosed of the type shown in US. Pat.No. 3,379,925, issued Apr. 23, 1968, to R.E. Edwards. Both these patentsare assigned to the assignee of the present invention. In the coaxialmagnetron art, therefore, it is desirable to provide improved tuningstructures as well as means for dither tuning which will have linear andreproducible tuning characteristics.

In the circular cavity mode under consideration, namely the TE theelectric currents are circumferential around the cavity walls while themagnetic fields are transversely disposed in a direction parallel to theaxis of the device. The large massive tuning structures vary thedistance between the upper and lower end walls of the cavity resonatorto reorient the field distributions of both the electric and magneticfields and thereby provide for the alteration of the resonant frequency.A lightweight tuning structure which avoids the difficulties of thelarge massive structures and provides for fine, as well as, dithertuning capability is, therefore, desirable for electromagnetic energypropagation devices and systems.

SUMMARY OF THE INVENTION The present invention provides a coaxialmagnetron having an outer cavity resonator with tuning means for varyingits dimension in and near the region of maximum electric field intensitywhen operated in the TE mode. In one embodiment mechanical means providefor reciprocating motion of split ring tuner structures having at leastone end anchored. The deformation of the ring tuner provides adissymmetry in the cavity geometry with the maximum excursion deformingthe substantially circular cavity to have a slightly ellipticalconfiguration. The introduction of conductive tuner material in thecavity alters the path of the electric currents. In an illustrativeembodiment a groove housing the tuning structure is provided by anannular wall structure girdling the outer cavity resonator walls. Thedepth of the groove provides the limits of the tuning structureexcursion. The absence of transverse components of current across thegroove housing the split tuning ring structures assures a continuance ofelectrical efficiency with the applicable structure. A tuning range ofup to 200 MHz has been demonstrated at different frequency bands withthe doubly actuated split ring structures. Multiple tuning structureassemblies will effectively double the tuning range. Linearity andreproducibility of the tuning characteristics over a substantial portionof the frequency tuning band has also been demonstrated. Coupling ofdither tuning mechanisms such as a high speed motor-driven eccentricdrive and resolver with the disclosed structure will provide forfrequency agility in a transmission system.

BRIEF DESCRIPTION OF THE DRAWINGS Details of illustrative embodiments ofthe invention will be readily understood after consideration of thefollowing description and reference to the accompanying drawings,wherein:

FIG. 1 is a diagrammatic cross-sectional view of the principalcomponents embodied in the present invention; a

FIG. 2 is a front elevational view of a coaxial magnetron embodying thepresent invention;

FIG. 3 is a side elevational view of the embodiment shown in FIG. 2;

FIG. 4 is a curve illustrating the tuning characteristics of anillustrative embodiment of the invention;

FIG. 5 is a cross-sectional view taken along the lin 5-5 in FIG. 3;

FIG. 6 is a cross-sectional view taken along the line 6--6 in FIG. 5;

FIG. 7 is a cross-sectional view taken along the line 7 -7 in FIG. 3;

FIG. 8 is a vertical cross-sectional view taken along the line 8-8 inFIG. 2;

FIG. 9 is anelevation viewed in the direction indicated by the line 99in FIG. '7;

FIG. 10 is an elevation view of an alternative mechanical actuatingstructure for the embodiment of the invention; and

FIG. 11 is adiagrammatic representation in section of an alternativeembodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS. 2 and 3 theillustrative coaxial magnetron comprises an inner and an outer resonantsystem housed within envelope 12. A mechanically actuated tuner assembly14 including motor driven means for action of the tuning structuresincludes a gear housing 16 and resolver means 18 for readout of thefrequency. A cathode support assembly 20 extends coaxially from theenvelope 12. Cooling fins 22 surround the envelope 12 and an outputwaveguide window assembly 24 for coupling of the electromagnetic energyto the utilization load is also provided. The magnetic fieldproducing-means 28 includes substantially C-shaped permanent magnets 30and 32 which contact inner pole piece members (not visible in theseviews). The magnetic field extends parallel to the axis of the deviceand the electric field is oriented transver- 'sely thereto to providefor crossed field interaction in the region between the cathode and theanode members. The embodiment of the invention includes mechanicalactuating means 34 with intermediate mechanical coupling means fortranslation of motion from the tuner assembly 14 and gear housing 16into reciprocal motion of the tuner structure.

The novel concept and the principal components of the invention arediagrammatically illustrated in FIG. 1 which will now be described. Theinner resonant system 38 includes a cathode member 40 centrally disposedwithin an array of circumferentially disposed anode vane elements 42extending radially from common boundary wall 44. A plurality of cavityresonators 46 are defined between the anode elements. Alternate slots 48provide for coupling of the pi-mode generated energy in the inner systemto the outer coaxial cavity resonator 50 defined by the common boundarywall 44 and an external cylindrical wall member 52. The outer cavityresonator system is dimensioned to operate in the TE mode.

A plate member 54 is axially translated within the cavity resonator 50to tune the magnetron over a broad frequency band. Suitable mechanicalactuating mans,

such as rods 56, are joined by a yoke 58 to suitable drive means. Asplit ring tuner structure 60 is provided within a groove 62 disposed ata point near the middle of the wall member 52 where the electric fieldintensity is at the maximum value. The deformation of the ring tuner 60provides for introduction of a conductive material within the cavity andprovides a varying path for the electric currents which, as noted forthe TE mode, are circumferential along the wall 52 of the coaxial cavityresonator 50. The depth of the groove 62 determines the excursion of thetuner structure. Rapid deformation of the external cavity wall contourin the been shown to have similar linear tuning ranges over up to 200MHz at other bands. With motor driven dither actuator means, to behereinafter described, coupled to the disclosed tuning structure andoperated at speeds of up to 12,000 r.p.m.s an excursion of the tuningrange of 200 cycles per minute will result.

Further details of the illustrative embodiment shown in FIGS. 2 and 3will now be described with reference being directed to FIGS. 5-9,inclusive. Envelope 12 is defined by annular end wall members 66 and 68hermetically sealed to outer cylindrical wall member 52. The anode vaneelements 42 are appended to the common anode boundary wall 44 and extendradially inwardly to define therebetween cavity resonators 46 of theinner resonant system.

Cathode 40 is supported axially by the cylindrical support assembly 20which includes a tubular member 70 and is secured to magnetic inner polepiece member 72. Electrical leads for energizing cathode heater 74, aswell as the high voltage leads, are introduced through the cathodesupport assembly 20 to the appropriate anode and cathode members. Thepreviously described magnetic circuit producing means 28 contacts innerpole piece member 72 as well as pole piece adapters 76.

The outer resonant system includes coaxial cavity resonator 50 definedby the common anode boundary wall 44 and the outer cylindrical wallmember 52. Slots 48 in wall 44 provide for the coupling and locking ofthe energy between inner and outer resonant systems. Any degenerateenergy modes are suppressed by annular lossy member 78 disposed withinend wall member 66 and member 80 adjacent to the quarter-wavelengthchannel choke 82 in end wall member 68. The external coaxial cavityresonator 50 is coupled through iris 84 and a transformer section to theutilization load by means of output waveguide assembly 24. An exhausttubulation 86 in outer wall member 52, as well as, a mounting and anchorplate 88 together with anchor screw means 90 and 92 comprise theremainder of the coaxial magnetron structure.

An axially translated plate member 94 for broad frequency tuning isactuated by the tuning mechanism 14 including a worm gear arrangement 96together with post members 98 with a deformable bellows arrangement 100secured between the tuner mechanism and a movable support member 102. Aslot mode absorber assembly 104 is also axially translated adjacent tothe ends of the slots 48 in the manner described in detail in thepreviously referenced pending United States patent application, Ser. No.147,914.

The split ring tuner structure 106 is disposed within groove 108 formedin outer wall member 52. In FIG. 8 the detailed embodiment is shown withthe broad tuning plate member 94 in two stages of operation to assist inan understanding of the invention. Components which are involved inmovement are shown in the lefthand portion as being at rest. Componentsshown in the right-hand portion and designated by the suffix a" are inthe tuned position.

The tuning structure 106 comprises split ring members and 107 anchoredat one end adjacent window assembly 24 to the wall structure of groove108. The opposing ends 105' and 107 are coupled to actuator means 34 byreciprocating blade members 110 introduced through slot 112 in cavityresonator wall 1 vide for electrically isolating the ring member fromthe actuator. In FIG. 5 the right-hand portion of the illustrationrepresents the tuning ring members disposed entirely within groove 108and, therefore, not perturbing the electric currents in the cavityresonant wall. The left-hand portion represents the tuning ring membersin full tuning position extending within the cavity resonator 50. Thepoint of maximum electric field intensity, as previously noted, isapproximately at the midpoint of wall 52. The blade members in theposition designated 110a, therefore, represent the innermost position asdetermined by the actuating mechanism. The split tuning ring membersanchored at one end upon being deformed have a slight elliptical contourin the essentially circular cavity geometry at the midpoint region.

In an exemplary embodiment of the invention the split tuning ringmembers were fabricatedof a rigid metallic material such as, forexample, the alloy comprising percent tantalum and 90 percent tungsten.Copper plating preserves the overall electrical circuit efficiencies ofthe cavity resonator structure. Each of the tuning ring members foranx-band embodiment have a width of 0.050 inches and a height of 0.100inches.

Ring damping structures 114 are provided a'pproximately 180 apart byhousing members .116 each providing two tiers of dielectric rod members118 adapted to contact opposing sides of tab portions 120. As shown inFIG. 6 the dielectric members 118 support the tab portions and therebydampen any vibrations for good radial stability in dither tuningapplications.

Reciprocating blade members 110 are actuated by means including pivotedcam follower members 122 now to be described with reference beingdirected to FIG. 7. Each of the members 122 are supported by a centralpivot 124 and surrounding ball bearing arrangement 126 secured to ahousing member plate 128. A rocker type motion will result with arms13.0 and 132 providing a reciprocating motion about the central pivotaxis. Each of-the arms 130 and 132 carry a cam roller 134 and 136adapted to contact adjacent bearing surfaces. g

Follower member structure 138 includes tubular members 140 having pistontype members 142 disposed at the inner end to contact reciprocatingblade members 110 disposed within a notch 143. Members 140 are providedwith threaded bearing members 144 and are suitably adjusted to attainthe desired stroke of the actuating means. An inner bearing surfacemovement of the movable armsl32.

Actuation of the ring tuner structures is provided by verticallydisposed linear control member 158 carrying onits inner end a bearingsurface 160 which contact rollers 134. The outer .end contactseccentrically motor 164. In FIG. 7 the right-hand portion represents therest position with the tuning ring members supported wholely within thegroove 108. The right-hand portion represents the rest tuning positionwith the ring members disposed within the groove 108. The linear controlmember 158 is shown in the downward thrust position and the bellows 152are compressed. In the left-hand portion or full tuning position thelinear con- 7 trol member is in the upward thrust position with thebellows 152 extended to urge the reciprocating blade members to theposition within the circular cavity resonator. All the pertinent movablestructure, therefore, reflecting the fully tuned position on theleft-hand portion of the illustration has again been designated by thesuffix a" to assist in an-explanation of the invention. In the exemplaryembodiment the tuning range, as described in FIG. 4, was achieved withan actuating means having a stroke of approximately 0.130 inches foreach tuning cycle with the 'ring tuner structures moving transverse tothe axis of the cavity resonator.

Referring now to FIG. 9 the top view illustrates motor driven tunerassembly means 14 including eccentric bearing members 162 and 163mounted on a shaft 166 which is actuated by a motor 164. All thecomponents are supported on a plate member 168. The worm and geararrangement 96 for driving the broad tuning plate member 94 is supportedbeneath plate 168 as indicated by the dashed lines in this view. Theoverall stroke for a linear control member 158, in an exemplaryembodiment to cover the described tuning range, was approximately 0.090inches. Bearing members 162 and 163 are eccentrically mounted on theshaft 166 so that, initially, bearing 162 picks up the linear controlmember 58 and upon completion of the tuning cycle the inner bearingmember 163 contacts this linear control member. The assembly iscompleted by a resolver means 170 controlled by shaft 166 to provide fordirect readout of the fine tuning frequencies over a substantial portionof the tuning range. In present day apparatus a resolver-having directfrequency readout is readily available. In this view the position of thelinear co'ntrol member 158 has been shown by dashed linesto indicate therelationship with eccentrically mounted bearing members 162 and 163.

In FIG. 10 alternative actuating means for movement of the split tuningring members is indicated and will now be described. Yoke arrangement172 comprising scissors-type arm members 174 and 176 are united by acentral pivot member 178 Eccentrically mounted bearing member180 ismounted on a shaft 182 driven by motor 184. The displacement of bearingmember 180 results in reciprocating movement of handles 186 and 188attached to the outer ends of arms I74 and 176. The inner ends of thereciprocating scissors-type structure 172 provides for reciprocatingmovement of mounted bearing'members 162 which are driven by a v theinner ends 190 and 192 of the arm members. Piston actuators 194 and 196suitably spring-loaded as by a member 204. A second tuning ring member206 may also be disposed within the groove 202. By providing for a widerdimension of the tuning ring 206 the tuning range capability may bedoubled. A frequency range, therefore, of up to 400 MHz could berealized over desired frequency bands which is particularly useful inthe dither tuning structures for frequency agility systems.

Another application of the disclosed tuning structure resides inautomatic temperature compensation over an operating band offrequencies. Generally in resonant cavities different metals areemployed having different coefficients of expansion to reduceperturbation of resonant frequencies due to thermal absorption. Byproviding a suitable liquid in the bellows, the thermal effects on the Qof the cavity can be effectively compensated for by expansion andcontraction of the liquid which will move the tuning structure in andout of the cavity interior. Such movement, as herein described, variesthe cavity resonance by introducing a dissymmetry in the electricalcurrent bearing surfaces.

In addition to the disclosed material composition of the split tuningring members, numerous other metals, such as molybdenum, which arecapable of withstanding high bake out temperatures may be utilized inthe practice of the invention. Numerous other variations, alterations ormodifications will also become apparent to those skilled in the art. Itis intended, therefore, that the foregoing description of the preferredembodiments be considered in the broadest aspects and not in a limitingsense.

Iclaim: 1. A crossed field device comprising: a cathode; an innerresonant system including a plurality of spaced anode members supportedby a common boundary wall and defining therebetween cavity resonatorssurrounding said cathode to generate electromagnetic energy; an outerresonant system including a wall member defining with said boundary walla coaxial cavity resonator adapted to be resonant over a frequency band;

means for producing crossed electric and magnetic fields; and

means for tuning the resonant frequency of said coaxial cavity resonatorby introducing a physical dissymmetry in the cavity wall geometry in there one end anchored.

3. The device according to claim 2 wherein said ring members areactuated reciprocally by means coupled to their free ends.

4. The device according to claim 3 wherein said ring members are adaptedto be spring-loaded.

5. The device according to claim wherein said ring members are supportedat points intermediate the anchored and free ends by stabilizing andvibration damping means.

6. The device according to claim 1 and means including an axiallytranslated tuning member dis osed within sald coaxia cavity resonator tovary t e resonant frequency.

7. A coaxial magnetron comprising:

a cathode;

an anode member having a plurality of radially extending vane elementssupported by a common boundary wall and defining therebetween cavityresonators;

an outer cylindrical wall member defining with said boundary wall andopposing end wall members a coaxial cavity resonator adapted to beresonant over a frequency band in a predetermined electric and magneticfield operating mode;

said boundary wall having axially extending slots coupling energybetween said anode and coaxial cavity resonators;

means for producing crossed electric and magnetic means for tuning theresonant frequency of said coaxial cavity by introducing a physicaldissymmetry in the outer wall member geometry in the region of maximumelectric field intensity;

and means for actuating said tuning means in a direction transverse tothe axis of said coaxial resonator.

8. The magnetron according to claim 7 wherein said coaxial cavityresonator is operated in the TE mode.

9. The magnetron according to claim 7 wherein said tuning means comprisesplit ring members housed within a groove defined near the midpoint ofthe axial length of said outer wall member.

10. The magnetron according to claim 9 wherein said split ring memberscomprise a substantially rigid refractory conductive metallic material.

11. The magnetron according to claim 10 wherein said split ring membersare fabricated of a tantalumtungsten alloy.

12. The magnetron according to claim 7 and a plate member axiallytranslated within said coaxial cavity resonator to vary with one of saidend wall members the axial frequency determining dimensions.

1. A crossed field device comprising: a cathode; an inner resonant system including a plurality of spaced anode members supported by a common boundary wall and defining therebetween cavity resonators surrounding said cathode to generate electromagnetic energy; an outer resonant system including a wall member defining with said boundary wall a coaxial cavity resonator adapted to be resonant over a frequency band; means for producing crossed electric and magnetic fields; and means for tuning the resonant frequency of said coaxial cavity resonator by introducing a physical dissymmetry in the cavity wall geometry in the region of maximum electric field intensity; said tuning means being adapted for movement along a path transverse to the axis of said coaxial cavity resonator.
 2. The device according to claim 1 wherein said tuning means comprise split ring members having at least one end anchored.
 3. The device according to claim 2 wherein said ring members are actuated reciprocally by means coupled to their free ends.
 4. The device according to claim 3 wherein said ring members are adapted to be spring-loaded.
 5. The device according to claim 3 wherein said ring members are supported at points intermediate the anchored and free ends by stabilizing and vibration damping means.
 6. The device according to claim 1 and means including an axially translated tuning member disposed within said coaxial cavity resonator to vary the resonant frequency.
 7. A coaxial magnetron comprising: a cathode; an anode member having a plurality of radially extending vane elements supported by a common boundary wall and defining therebetween cavity resonators; an outer cylindrical wall member defining with said boundary wall and opposing end wall members a coaxial cavity resonator adapted to be resonant over a frequency band in a predetermined electric and magnetic field operating mode; said boundary wall having axially extending slots coupling energy between said anode and coaxial cavity resonators; means for producing crossed electric and magnetic fields; means for tuning the resonant frequency of said coaxial cavity by introducing a physical dissymmetry in the outer wall member geometry in the region of maximum electric field intensity; and means for actuating said tuning means in a direction transverse to the axis of said coaxial resonator.
 8. The magnetron according to claim 7 wherein said coaxial cavity resonator is operated in the TE011 mode.
 9. The magnetron according to claim 7 wherein said tuning means comprise split ring members housed within a groove defined near the midpoint of the axial length of said outer wall member.
 10. The magnetron according to claim 9 wherein said split ring members comprise a substantially rigid refractory conductive metallic material.
 11. The magnetron according to claim 10 wherein said split ring members are fabricated of a tantalum-tungsten alloy.
 12. The magnetron according to claim 7 and a plate member axially translated within said coaxial cavity resonator to vary with one of said end wall members the axial frequency determining dimensions. 